source:
asp3_tinet_ecnl_arm/trunk/musl-1.1.18/src/math/cosh.c@
377
Last change on this file since 377 was 352, checked in by , 6 years ago | |
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File size: 764 bytes |
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1 | #include "libm.h" |
2 | |
3 | /* cosh(x) = (exp(x) + 1/exp(x))/2 |
4 | * = 1 + 0.5*(exp(x)-1)*(exp(x)-1)/exp(x) |
5 | * = 1 + x*x/2 + o(x^4) |
6 | */ |
7 | double cosh(double x) |
8 | { |
9 | union {double f; uint64_t i;} u = {.f = x}; |
10 | uint32_t w; |
11 | double t; |
12 | |
13 | /* |x| */ |
14 | u.i &= (uint64_t)-1/2; |
15 | x = u.f; |
16 | w = u.i >> 32; |
17 | |
18 | /* |x| < log(2) */ |
19 | if (w < 0x3fe62e42) { |
20 | if (w < 0x3ff00000 - (26<<20)) { |
21 | /* raise inexact if x!=0 */ |
22 | FORCE_EVAL(x + 0x1p120f); |
23 | return 1; |
24 | } |
25 | t = expm1(x); |
26 | return 1 + t*t/(2*(1+t)); |
27 | } |
28 | |
29 | /* |x| < log(DBL_MAX) */ |
30 | if (w < 0x40862e42) { |
31 | t = exp(x); |
32 | /* note: if x>log(0x1p26) then the 1/t is not needed */ |
33 | return 0.5*(t + 1/t); |
34 | } |
35 | |
36 | /* |x| > log(DBL_MAX) or nan */ |
37 | /* note: the result is stored to handle overflow */ |
38 | t = __expo2(x); |
39 | return t; |
40 | } |
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